In the field of Thin Film Technology, used extensively in manufacture of integrated circuits, requirements for thinner deposition layers, better uniformity over larger surfaces, and larger production yields have been, and are, driving forces behind emerging technologies developed by equipment manufactures. As semiconductor devices become smaller and faster, the need for greater uniformity and process control in layer thickness, uniformity, resistivity and other film properties rises dramatically.
Various technologies are well known in the art for applying thin films to substrates in manufacturing steps for integrated circuits (ICs). Among the more established technologies available for applying thin films is Chemical Vapor Deposition (CVD), which includes Plasma Enhanced Chemical Vapor Deposition (PECVD). These are flux-dependent applications requiring specific and uniform substrate temperature and precursors (chemical species) to be in a state of uniformity in the process chamber in order to produce a desired film properties on a substrate surface. These requirements become more critical as substrate size increases, and as device size decreases (i.e. line width) creating a need for more complexity in chamber design and gas flow techniques to maintain adequate uniformity.
CVD systems use a variety of known apparatus for delivering precursor gases to target substrates. Generally speaking, gas delivery schemes for CVD and PECVD processes are designed specifically for one particular application and substrate size. Therefore variations in theme of such delivery apparatus and methods will depend on the particular process parameters and size of substrates being processed in a single reactor. Prior art gas manifolds and diffusers have been manufactured from a variety of materials and are widely varied in design. For example, some gas delivery manifolds are long tubes that are either straight or helical with a plurality of small, often differently sized, gas delivery holes spaced longitudinally along the manifold. Most diffusers and showerheads are basically baffle-type structures having a plurality of holes placed in circular or spiral type arrangements on opposite facing plates or surfaces. Often the holes are contained in a series of expanding radii circles on each plate. Often such apparatus is adapted only for one type of process and cannot be used with other processes using the same CVD equipment.
One characteristic that is generally required in CVD gas delivery apparatus is that hole sizes and spacing between the holes is strictly controlled such that a uniform gas distribution or zone is maintained over a particular surface area. Uneven gas flow often results if some holes are inadvertently made too large in comparison with a mean size, or placed in wrong positions. If a larger substrate is used in a same or different chamber, then the gas delivery apparatus must often be exchanged for one that is designed and adapted for the variance in substrate size and/or chamber parameters. Improvements made to manifold and diffuser designs depend largely on empirical methods in the field resulting in numerous cases of product expenditure through batch testing.
Uniform gas delivery remains a formidable challenge in the CVD processing of substrates. If gas delivery uniformity cannot be strictly controlled, layer thickness will not be uniform. The problem progresses with increased target size and as more layers are added. Moreover, many substrates to be coated already have a complex topology introducing a requirement for uniform step coverage. PECVD in many cases has advantages over CVD in step coverage by virtue of delivering more reactive chemical precursors, energized by the plasma. However, to this date, methods for gas delivery in CVD, including PECVD type systems, have much room for improvement.
One problem with many diffusing showerhead systems relates to limited gas flow dynamics and control capability. For example, gas delivered through a typical showerhead covers a diffusion zone inside the chamber that is produced by the array of diffusion holes placed in the showerhead. If a system is designed for processing a 200-mm wafer or wafer batch, the gas diffusion apparatus associated with that system will produce a zone that is optimum for that size. If the wafer size is increased or reduced beyond the fixed zone capability of a particular showerhead, then a new diffusion apparatus must be provided to accommodate the new size. There are typically no conventions for providing more than a few zones or for alternating precursor delivery for differing size substrates in one process.
In an environment wherein different sizes of substrates are commonly processed, it is desired that diffusing methods and apparatus be more flexible such that multi-zone diffusing on differing size substrates is practical using one showerhead system. This would allow for less downtime associated with swapping equipment for varying situations, and better uniformity by combining and alternating different zones during diffusion. Prior art diffusing methods and apparatus do not meet requirements for this type of flexibility.
Another problem in this technology is that various gases of different characteristics are mixed for a particular process. There are variations in density, temperature, reactivity and the like, such that perfect uniformity in gas mixture composition and density at delivery still does not produce precise uniformity in layer deposition. In some processes an intentional non-uniformity of gas delivery will be required to produce layer uniformity.
What is clearly needed is an enhanced precursor-delivery apparatus and method that allows for a strict and combined control of gas distribution over multiple target zones in a reactor, and has several degrees of freedom in gas mixing, delivery, and uniformity control. Such a system would provide a capability for adjusting gas flow in a manner that point-of-process reaction uniformity may be achieved, providing superior film property uniformity. Such a system may be adapted to function in a wide variety of CVD and PECVD applications.